The present invention relates to the preservation of paint in containers. However it could equally well be applied to the preservation of any other fluids and/or solids within an enclosed circular container or can, or other protective fluids such as varnish and lacquers. Although the following description deals with paint it is therefore to be understood that it is not intended to limit the invention to preserving of paints.
The following description refers to a paint sealer as a fluid cover. It is however to be understood that this relates to the same device and it is not intended to distinguish one from the other. Further, other terms to describe the invention may equally well be used, such as a lid or a seal. The present invention therefore relates to a device that is placed on top of paint in a can that has been partially used and that seals the paint from the outside air.
Paints are typically housed in cylindrical metal containers or cans. The cans come in a range of sizes, with the bigger sizes in Australia typically being cans whose volume is 4 litres, 10 litres or 20 litres.
The sealable top lid prevents paint from drying or skinning when a can is nearly full but as the contents are used over time the ratio of paint to residual air in the can changes. The air is responsible for allowing the paint to partially evaporate, dry out, or form a thick skin on top. Whilst the problem in commercial applications may not be as great, most paint being used within several days, paint may be stored in cans for years to be used either for re-coating or for touching up an existing area.
In response to this problem, there have been proposed many devices that protect the paint regardless of its level within a can. Some of these devices are quite complex mechanical contraptions that by their very nature are difficult to use and are expensive. Yet other devices provide for floating disks that provide separation of the partially filled contents of a can from the air above while in storage. These disks are generally circular and are designed to fit within the can and float upon the residual contents of the can. Some of these have included features for increasing the friction between the device and the can walls but they do not entirely remove unwanted air from being in contact with the paint nor do they accommodate the can from being tilted.
In addition, only a few of these floating disk or fluid cover solutions have understood the need to achieve a complete seal of the paint. A fluid cover that merely passively floats upon the surface of paint will not prevent the loss of evaporative components from around the edge of the fluid cover. Evaporates take gaseous form and are lighter than air, thereby passing into the vacant portion of the can. The larger the volume of air in the can, or the more frequently the can is opened the more serious becomes the loss of evaporates. Also, none of these devices have addressed the need for a fluid cover that accommodates cans that may not be perfectly circular and whose cross-sectional shape may vary.
The author is aware of only one device that has been designed to achieve a complete seal. This device, described in U.S. Pat. No. 4,416,387 by D'Antonio, relies on the paint itself to fill the gaps at the perimeter of the device in order to properly attain a seal. That is, the paint at the edge of the fluid cover dries thereby protecting the paint within the can. A partial vacuum then assists to keep the fluid cover in place. To accomplish this, D'Antonio provides for an outer flange having a slightly larger diameter than the can. There are several difficulties in the aforementioned design by D'Antonio.
Firstly the fluid cover does not accommodate cans whose cross-sectional size may vary. The fluid cover as taught by D'Antonio includes a central portion having a raised central axial squeeze section, a flat circular channel surrounding said flat portion and defined by two upward walls, a narrow sealing flange then extending horizontally from the outer one of those two walls. Such an arrangement does not allow for flexibility of the fluid cover in the horizontal plane, which is necessary in cans whose cross-sectional shape is not perfectly circular. D'Antonio's seal is simply incapable of flexibly expanding or contracting to take up the irregularities encountered in typical paint can wall shapes. It is not uncommon for can diameters to vary by upwards of 1.0 mm or so. The teaching of the low profile channel by D'Antonio in fact helps to maintain the shape of the fluid cover. In addition, the method of forming the device described by D'Antonio involves a heat treatment of plastic film that upon withdrawal from the die cools and shrinks. It is well known that the pulling of the device to achieve a raised central air expulsion portion will cause outer perimeter shrinkage that is unevenly distributed about the circumference of the device. This means that a non-circular seal will be inserted into a non-circular can, the consequences being that random circumstance will determine whether or not a good seal is obtained. If the fluid cover is manufactured of non-circular shape, as is common in low cost high volume plastic die operations, this further limits the usefulness of the fluid cover as taught by D'Antonio.
Secondly, the device taught by D'Antonio requires that there be a wetting of the seal edge by the can contents in order to attain a proper seal. The paint then dries meaning that a can whose contents are often accessed ends up with dried paint layers on the side. In addition, even where the seal matches perfectly the internal configuration of the can there is no means provided for retaining the seal against the can wall during any subsequent tilting of the can. Mere contact does not achieve this, and partial vacuum alone will not force adherence between two bodies while greater force than the friction so obtained is brought to bear. The fluid cover taught by D'Antonio therefore does not assist in securely sealing the paint when the can is tilted as may be expected during normal handling of the can.
Accordingly none of the prior art known to the applicant provides a fluid cover that successfully seals a liquid in a partially empty cylindrical can even when the can is tilted after applying the fluid cover, nor are they capable of accommodating cans whose internal shape may not be suitably circular.
It is the object of the present invention to overcome at least some of the abovementioned problems or provide the public with a useful alternative.
It is a further object of the present invention to provide a paint fluid cover for use in a can that seals paint even where the can walls may not be perfectly circular and where the fluid cover remains in place during normal carrying and tilting of the can.